On the evening of September 17, Bill de Blasio declared his primary victory, formally becoming the Democratic nominee and front-runner for New York City mayor. Standing behind him, one of the few invited onstage for this momentous event, was a friend, an adviser, a strategist, and a campaigner — Bertha Lewis, former head of ACORN.

De Blasio, the truest of progressives — who turned some heads recently when he defended his support of the Sandinista government in Nicaragua in the 1980s — has been connected for more than a decade with the now infamous Association of Community Organizations for Reform Now and its associates, especially and most notably former ACORN “chief organizer” Bertha Lewis.

Bertha Lewis and ACORN, which made headlines in 2009 when secret videos revealed that its employees were complicit in illegal activity, had connections with de Blasio as far back as the early 1990s, when David Dinkins was mayor of New York. De Blasio served as an aide to Dinkins in City Hall.

“I got to encounter [de Blasio] initially when he was in the Dinkins administration,” Lewis told me in an interview. “The late Jon Kest, who was the head of New York ACORN . . . had a personal relationship with Bill, and over the years my relationship with him grew.”

Lewis really got to know de Blasio after he was appointed to serve as the highest official in the tri-state area for the U.S. Department of Housing and Urban Development. This connection would only grow stronger over the following 16 years, to the current mayoral campaign.

Lewis was open in confirming this connection. “I knew Bill when I was a part of ACORN,” Lewis said. “We [ACORN] knew Bill when he worked for HUD. . . . We knew Bill when he worked on Hillary’s Senate campaign, and then we knew him when he wanted to run for City Council and when he wanted to run for public advocate.”

De Blasio worked for Hillary Clinton when she successfully ran for Senate in 2000. He was a New York City Council member from 2001 to 2009, and has been New York City’s elected public advocate since 2009.

“So we go back a long time, interacting and working on issues,” Lewis added.

When I asked Lewis how often she meets with de Blasio, she responded that she started meeting with him regularly a couple of years ago. “I would meet with Bill on a regular basis to talk about issues. . . . Definitely his role as public advocate and also his role when he was in the City Council on the General Welfare Committee,” she said. “I might meet with him maybe four, five, six times a year.”

When he decided to run for mayor, these meetings became more frequent. “We used to meet every month, along with other folks,” Lewis said, “to talk about issues and strategy, and the structure of the campaign, and outreach, and constituents, and get-out-the-vote. We met a lot of times during the primary.”

Beyond her direct connections with de Blasio, Lewis also actively campaigns for him informally. She said she encourages her friends and colleagues to support de Blasio. “I tell them ‘this is who I think you should support, and here’s why.’”

While de Blasio was unavailable for comment, the New York Postreported that de Blasio is proud to stand with the former leader of ACORN and her organization. “Bertha Lewis is one of the city’s most passionate and effective progressive leaders, and I’m proud to have worked with her for years,” de Blasio said.

Lewis, a longtime progressive and community organizer, rose to national prominence during her time as “chief organizer,” or CEO, of ACORN, a now defunct leftist community organization.

It was during Lewis’s tenure as chief organizer that ACORN faced a scandal brought to light by conservative journalists James O’Keefe and Hannah Giles, who shot secret videos showing ACORN employees advising the playacting pair on how to hide prostitution activities and avoid taxes.

According to Matthew Vadum — a journalist, author, and senior editor at the Capital Research Center — Lewis attempted to cover up this scandal, “claiming over and over again that ACORN employees shown in the videos were rogue actors.” Vadum’s 2011 book, Subversion, Inc., details the detrimental effects of left-wing community organizations, most notably ACORN.

Every time Lewis denied a video, Vadum told me, the news “would put out another video the next day until eventually people started getting the message.”

ACORN subsequently attempted to clear its name with two probes — one internal and another conducted in California by then–Attorney General Jerry Brown — both of which found no evidence of wrongdoing.

Vadum noted that both probes were conducted by left-wing friends of ACORN and, as he told me, “if you invite your friends to investigate you, chances are your friends aren’t going to find anything wrong with you.”

ACORN also had been consistently accused of voter-registration fraud, the charges arising every election cycle — including the years Lewis ran the organization.

Regardless of the result of the probes and other accusations, the damage was done, and Congress eliminated its funding of ACORN in 2009. The organization filed for bankruptcy in the fall of 2010.

But ACORN lives on. Judicial Watch, a conservative, nonpartisan watchdog group, released a report in August 2011 detailing the creation of one international, four national, and 18 statewide ACORN-affiliated organizations after ACORN fell.

The direct offspring of ACORN in New York, New York Communities for Change, formally endorsed de Blasio, as did the Working Families Party, cofounded by Bertha Lewis in 1998. Lewis was a co-chair in the Working Families Party and now is a district leader and part of the state committee.

Though Lewis reports that she hasn’t seen de Blasio much in the past couple of weeks, she has been in contact with his campaign team. When asked if she will meet with him to talk more in the future, she responded, “Oh, absolutely. Oh, absolutely.”

— Alec Torres is a William F. Buckley Fellow at the National Review Institute.